Method of manufacturing acetylene from hydrocarbons



United States Patent METHOD OF MANUFACTURING ACETYLENE FROM HYDROCARBONS Shigeru Tsutsumi, Osaka, and Tsukumo Tomonari,

Ryogen-Mura, Muko-Gun, Japan, assignors to Kurashiki Rayon Company Limited, Kurashiki, City, Girayama Prefecture, Japan No Drawing. Application January 6, 1955 Serial No. 480,276

1 Claim. (Ci. 260-679) This invention relates to a method of manufacturing acetylene from hydrocarbons more particularly from saturated hydrocarbons such as petroleum, and is to provide a new thermal cracking method. 7

; An object of this invention is to manufacture acetylene from hydrocarbons with good yield and at a low cost. Another object'of this invention is to lower the temperature of thermal cracking and to facilitate the operation by suppressing the formation of byproducts, especially hydrogen.

Inorder to attain the objects, this invention essentially consists of a combination of two processes, which is characterized in that the first process in which hydrocarbons mainly consis'tingof saturated hydrocarbons such as petroleum are cracked to produce a gas which is rich in olefine content such as ethylene, propylene and the like at a temperature of 700 C.-900 C. employing a catalyst selected "from the group consisting of copper, nickel, chromium and nickel-chrome-steel, and the second process in which said cracked gas is mixed with a diluent gas and. then. cracked to produce acetylene under a reduced pressure below 300 mm. at a temperature of l,000 C.- 1,200 C. employing molybdenum as a'catalyst. The produced acetylene is then concentrated and recovered from the cracked gas by a gas absorption or a solvent extraction method. I

--.-The methods of manufacturing acetylene from hydrocarbons,"which have heretofore been proposed are mostly thermal cracking of methane by an electric arc, partial oxidation or high temperature heating. Methane is less reactive than higher hydrocarbons so that it requires a high temperature above l,500 C. in order to promote its reactivity,and there .are some difliculties in carrying out the operation and in obtaining suitable refractory materials for the reaction furnace. It is possible to reduce the cracking temperature by using hydrocarbons, but'if the cracking temperature is excessively low there remains a too large amount of such heavy hydrocarbons, andif the temperature is raised in order to promote the crackingfof the heavy hydrocarbons, there occurs a large quantity of deposit of carbon and production of hydrogen due to the over-decomposition of hydrocarbon so that the yield decreases. This tendency will become more remarkable as the fractions of higher boiling point in the-'oil used increase and also when the fraction of higher boilingpo-int is used.

In order to avoidthe above difiiculties, the inventors consisting of copper, nickel, chromium and nickel-chromesteel? In this case, it is advisable to use a reduced pressure or to mix the gas with steam or other diluent gas if hydrocarbons having a higher boiling point are used.

2 ,838,584 Patented June 10, 1958 2 It is most advantageous to select the cracking conditions such that the olefin content, more particularly the ethylene content, in the cracked gas will become most predominant.

The cracked gas thus obtained is rich in olefins, more particularly in ethylene, and contains a certain quantity of heavy hydrocarbons varying in accordance with the kinds of raw material and the conditions of cracking, but having a very homogeneous composition compared with the starting materials.

Light oils such as n-hexane, cyclohexane and the like will produce easily gases containing olefins of 50 to 60 volume percent by thermal cracking under atmospheric pressure and at a temperature of 750 C.-800 C. If for instance n-hexane is heated and decomposed at 750 C. by employing a copper wire gauze as a catalyst, a gas containing 56% of oleiins is obtained by cracking.

, Other examples of thermal cracking with or without catalyst areas follows: The reaction tube has 20 mm. internal diameter, heating part of 800 mm. length and catalyst layer of 200 mm. length. The cracking is effected under a pressure of 300 mm. (mercury) at a temperature of 850 C. The volumes of cracked gas evolved are 7l0720 liters per 1 liter of reacted oil.

It is shown clearly in the above table that the catalyst is remarkably effective in the first cracking step to obtain a cracked gas which is rich in olefins.

The larger the olefin content in the cracked gas of the first cracking step is, the higher is the yield of acetylene obtained in the second process, so that it is most important to produce the cracked gas of high olefin content in the first step by a suitable selection of catalyst, temperature and time of cracking. For heavy oils, it is effective to carry out the cracking under reduced pressure below 300 mm., or from 200 to mm. and also with addition of diluent gas or steam.

In the second cracking step, the cracked gas of the first cracking step is diluted with a suitable amount of diluent gas (for example hydrogen, residual gas after acetylene extraction, or steam) in order to prevent the deposition of carbon and formation of hydrogen due to over-decomposition, and the mixed gas is subjected to thermal cracking under a reduced pressure below 300 mm. and preferably at a temperature higher than 900 C. and lower than 1200 C. employing molybdenum as a catalyst. As the result of experiments, the inventors have found that satisfactory results can be obtained at a temperature of 1,000" C. to l,l00 C. and sufiicient cracking can be effected up to the highest temperature of l,200 C. Under such a condition, acetylene can be obtained from amixture of hydrocarbons such as petroleum at a satisfactory yield with less carbondeposit and also less formation of hydrogen and methane.

The degree of dilution with a diluent gas depends on the olefin content, and it is necessary to use more diluent when the gas contains a large amount of heavy hydrocarbon.- A dilution of 3 to 7 times the volume is usually most suitable, though the dilution can be suitably selected.

The effects of different catalysts are shown in the following table. The gas which was produced in the first cracking step and contained 41% (volume) of olefins, was diluted with 6 times (volume) hydrogen, and passed at a flow rate of about 90 l./h. through porcelain tubes of 12 mm. internal diameter and the length of heating part of 300 mm., heated to 900 C., l,000 C., 1,100C. and 1,200 C. respectively under a pressure of 200 mm. (mercury). The results are shown in the following table where various catalysts were use in form of a Wire of 0.5 mm. diameter and 12 g. in weight, wound as a spiral coil.

The following results show the amount of acetylene in liters produced per 100 l. of starting gas (the cracked gas obtained in the first step) at different temperatures.

As it is apparent from the above table, molybdenum is the best catalyst, while tungsten gives relatively good results only at a higher temperature. The thermal cracking temperatures of 1,000 C. and 1,100 C. give better results, while at 900 C. the cracking is insuflicient and at 1,200 C. the cracking is rather excessive. From these results, it is clear that acetylene is produced not only from olefins, but also from paraflins.

In developing this invention to a commercial plant, the form or design of heaters of the two cracking steps is important. For the heating part of the first cracking step, a pebble heater system, in which pebbles coated with catalytic metal or its oxide are cycled between the heating part of pebbles and the cracking part of hydrocarbon, may be one of the most suitable systems. For the second cracking step, a refractory furnace composed of checkered refractory material is most suitable.

Besides petroleum distillates, decomposed petroleum gases, coke-oven gases, synthetic hydrocarbon gas produced during the manufacture of synthetic petroleum, and synthetic hydrocarbon (either in the gaseous or oily state) may be used as the starting material in carrying out the method of this invention. Since the use of raw material which can be easily converted to ethylene is most advantageous in carrying out this invention, it is desirable to use hydrocarbons having more than 2 and less than 15 carbon atoms.

Examples of the method of this invention are given below:

Example I n-Hexane was decomposed at 750 C. with copper wire gauze as a catalyst and a cracked gas containing 34.0% (volume percent) of ethylene and 18.0% of heavy hydrocarbon was obtained. The cracked gas was diluted with 6 times (volume) hydrogen and was thermally cracked at 1,050 C. under a pressure of 200 mm. with molybdenum as a catalyst, 71.0 liters of acetylene were obtained from 100 liters of the first stage cracking gas.

Example II Gas oil composed of fractions 31.8% boiling between 200-250 C., 48.4% boiling between 250300 C. and 16.3% boiling between 300-340 C. is preheated to a temperature of 500 C. and is mixed with steam superheated to a temperature of 500 C. in the weight ratio of 2 parts of oil to 1 part of steam. The gas mixture is passed through a stainless steel tube having 75 mm. internal diameter and heated for a length of 800 mm. packed with a nickel-chrome-steel wire net of 40 mesh, at a flow rate of about 3 liters of oil per hour, and heated to a temperature of 875 C. under reduced pressure of 200 mm. (mercury). In this process, 600 liters of cracked gas are generated per 1 liter of starting oil (790 liters per 1 liter of reacted oil). The by-produced oil and unreacted oil remaining after the reaction may be reused for cracking or for other purposes.

The gas generated in the first stage is diluted with 6 times (volume) hydrogen, and passed through a porcelain tube having 40 mm. internal diameter and heated for a length of 800 mm., and packed with a molybdenum wire coil as a catalyst, at a flow rate of about 760 liters of the gas mixture per hour, and heated to a temperature of 1,200 C. under reduced pressure of 200 mm.

- (mercury).

The compositions of the gas after the first stage process,

Acetylene generated in the second stage is concentrated and separated from the cracked gas components by an extraction method employing dimethyl formamide as a solvent. The yield of acetylene purified up to 99% is 500 liters from 1 liter of feed oil.

Example III Kerosene composed of fractions 12.5% boiling between 175-200 C., 72.5% boiling between 200-250 C. and 15.0% boiling between 250290 C. is preheated to a temperature of 500 C. and is mixed with steam superheated to a temperature of 500 C. in the weight ratio of 1:1. The mixed gas is passed through a porcelain tube of mm. internal diameter heated for a length of 800 mm. and packed with alumina pebbles of 8 mm. diameter coated with copper of 2% to the pebble weight, at a flow rate of about 2.5 liters of oil per hour, and heated to a temperature of 800 C. under reduced pressure of 300 mm. (mercury). The volume of cracked gas generated in this process is 580 liters per 1 liter of feed oil. The gas is diluted with 4 times (volume) off-gas recycled from the purification process, which is composed mainly of hydrogen and methane, and passed through a porcelain tube which has 40 mm. internal diameter and is heated over a length of 800 mm. packed with a molybdenum wire coil as a catalyst, at a flow rate of about 700 liters of the gas mixture per hour, and heated to a temperature of 1,100 C. under a reduced pressure of mm. (mercury). The compositions of the gas after the first stage process, the gas mixture and the gas after the second stage process are as follows (volume percentage) Gas after Gas mix- Gas after 1st stage, ture, 2nd

percent; percent stage,

percent A two-step process for the production of acetylene assess-1 I 5 from saturated hydrocarbons comprising passing in a References Cited in the file of this patent first step a stream 0f hYdl'OCfll'bOllS consisting essentially UNITED STATES PATENTS of saturated hydrocarbons having boiling points of about 175 to 350 C. at temperatures of about 700 to 900 C. 3 Winkle;- et and at a pressure below 300 mm. Hg over a catalyst se- 5 g g g g g g f: i lected. from e group consisting o ppe nickel, 213 2 s g 6 1949 chromlum and nlckel-chrome steel and then passmg the 2:582:016 Butcher Jan. 1952 effluent olefin-rich gas in a second step at a temperature of about 1000-1100" c. and at a pressure below 300 mm. 2,597,346 May 20, 1952 Hg over a molybdenum catalyst, thereby converting said 10 olefins substantially into acetylene. 

